It’s not easy to dye cotton fabric a washfast and lightfast blue with natural dyes (except with indigo and woad).
After reading that iron in the soil makes hydrangea flowers more blue, I wondered if iron mordant could help to fix the blue color to cotton fabric. And after some experiments with different mordants and modifiers and various natural blue dye materials, I’ve finally found out that red cabbage dye + iron mordant produces a beautiful washfast and lightfast blue! Yay!
This is my 18th century lappet cap. It’s suitable for a mid-18th century working woman. You can see working women wear lappet caps in these two paintings by Chardin and Hendriks. The lappets can also be pinned up, as here.